Photosensitive compositions and lithographic printing plates containing binary acetal polymers

ABSTRACT

Photosensitive compositions, useful in lithographic printing plates which can be developed with aqueous developing solutions, comprise a diazo resin and a binary acetal polymer which functions as a polymeric binder. The binary acetal polymers are comprised of recurring units which include two six-membered cyclic acetal groups, one of which is unsubstituted or substituted with an alkyl or hydroxyalkyl group and the other of which is substituted with an aromatic or heterocyclic moiety.

CROSS-REFERENCE TO RELATED APPLICATIONS

The novel binary acetal polymers utilized in the photosensitivecompositions and lithographic printing plates of this invention aredisclosed and claimed in copending commonly assigned U.S. patentapplication Ser. No. 738,068 filed Jul. 30, 1991, "Binary AcetalPolymers Useful In Photosensitive Compositions And Lithographic PrintingPlates", by John E. Walls.

FIELD OF THE INVENTION

This invention relates in general to novel photosensitive compositionsand in particular to the use of such photosensitive compositions inlithographic printing plates. More specifically, this invention relatesto photosensitive compositions comprising a diazo resin and a binaryacetal polymer and to lithographic printing plates comprising an imaginglayer formed from such photosensitive compositions.

BACKGROUND OF THE INVENTION

It is well known to prepare photosensitive compositions comprising aphotosensitive agent and a polymeric binder and to utilize suchcompositions in the preparation of lithographic printing plates whichcan be developed with aqueous neutral or alkaline developing solutions.In such compositions, it is common practice to utilize a diazo resin asthe photosensitive agent. The lithographic printing plates typicallycomprise a metal substrate, such as a substrate of anodized aluminum,which is coated with a photo-sensitive composition comprising the diazoresin, the polymeric binder and other ingredients such as colorants,stabilizers, exposure indicators, surfactants, and the like.

Many different polymers have been proposed for use as binders in theaforesaid photosensitive compositions. Particular advantages have beenachieved by the use of acetal polymers as described, for example, inU.S. Pat. Nos. 4,652,604, 4,741,985, and 4,940,646.

In U.S. Pat. No. 4,652,604, the acetal polymer contains acetal groups ofthree types, namely six-membered cyclic acetals, five-membered cyclicacetals and intermolecular acetals. In U.S. Pat. No. 4,741,985, theacetal polymer is a mono-acetal containing a six-membered cyclic acetalgroup. In U.S. Pat. No. 4,940,646, the acetal polymer contains vinylacetal units derived from an aldehyde that contains hydroxyl groups.

Acetal polymers can be advantageously utilized in lithographic printingplates in which the layer containing the acetal polymer and the diazoresin is the sole radiation-sensitive layer. They can also be usefullyemployed in so-called "dual layer" plates. In this type of lithographicprinting plate, a radiation-sensitive layer containing a diazo resin iscoated over an anodized aluminum support and a radiation-sensitive layercontaining a photocrosslinkable polymer is coated over the layercontaining the diazo resin. Such dual layer plates are described, forexample, in British Patent No. 1 274 017. They are advantageous in thatradiation-sensitive layers containing diazo resins adhere much morestrongly to most anodized aluminum supports than do radiation-sensitivelayers containing photocrosslinkable polymers. Thus, the enhancedperformance provided by photocrosslinkable polymers is achieved withoutsacrificing the excellent adhesive properties of diazo resincompositions.

While lithographic printing plates containing the acetal polymers of theprior art have generally performed in an effective manner, improvementin providing a more durable oleophilic image that is abrasion-resistant,resistant to chemical attack, capable of quick rollups and capable ofextended press performance, has remained a critical need in the art.Accordingly, it is toward the objective of providing improvedphotosensitive compositions and improved lithographic printing plates,capable of effectively meeting the needs of the lithographic printingplate art, that the present invention is directed.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a photosensitivecomposition comprising a diazo resin and a binary acetal polymer of thestructure described herein. In a second embodiment, the invention isdirected to a lithographic printing plate comprising an imaging layerformed from this photosensitive composition.

The binary acetal polymers utilized in this invention, which aredisclosed and claimed in the aforesaid copending U.S. patent applicationSer. No. 738,068, have recurring units represented by the formula:##STR1## wherein R₁ is --H, --C_(n) H_(2n+1) or --C_(n) H_(2n) --OHwhere n=1-12 ##STR2## where R₃ is ##STR3## and x=0-8 m=0-8

y=0-8

p=0-8

R₄ =--H, --R₅, ##STR4## in which Y=--O--, --S--, ##STR5## --CH₂ --,--NH-- or R₅ =--OH, --CH₂ OH, --OCH₃, --COOH or --SO₃ H

z=1 to 3

and n₁ =0-25 mole %, preferably 5 to 15 mole %

n₂ =2-25 mole %, preferably 5 to 15 mole %

n₃ =10-60 mole %, preferably 15 to 35 mole %

n₄ =35-80 mole %, preferably 45 to 70 mole %

As indicated by the above structural formula, the binary acetal polymersdescribed herein can be trimers, in which the recurring unit comprises avinyl acetate moiety and first and second cyclic acetal groups, ortetramers in which the recurring unit comprises a vinyl alcohol moiety,a vinyl acetate moiety and first and second cyclic acetal groups.

Both of the acetal groups are six-membered cyclic acetal groups, one ofthem is unsubstituted or substituted with an alkyl or hydroxyalkyl groupand the other is substituted with an aromatic or heterocyclic moiety.

The novel binary acetal polymers described herein provide lithographicprinting plates characterized by improved abrasion-resistance, improvedresistance to chemical attack, extended press performance and enhancedrollup properties in comparison with the acetal polymers of the priorart. Lithographic printing plates utilizing the novel binary acetalpolymers described herein as polymeric binders also have the importantadvantage that they can be processed in aqueous alkaline or neutraldeveloping solutions containing very low concentrations of organicsolvents. This is highly advantageous in view of the high costs andenvironmental concerns associated with the use of organic solvents.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The novel binary acetal polymers described herein can be prepared byhydrolyzing polyvinyl acetate, or by starting with partially hydrolyzedpolyvinyl acetate, i.e. polyvinyl alcohol, and reacting it with twodifferent aldehydes to thereby form a binary acetal. Suitable techniquesfor forming polymers of this type are known to those skilled in the art.Thus, for example, the binary acetal polymers can be prepared by anemulsion condensation wherein, as the solubility of the startingmaterial changes from water-soluble to solvent-soluble as a result ofthe formation of the acetal groups, the product forms an emulsionbecause of its lack of solubility in water. In this method, theparticles are prevented from aggregating by use of a surfactant. Analternative method is to compensate for the change in solubility of thestarting material from water-soluble to solvent-soluble by maintaining ahomogeneous solution through the continual addition of an appropriatesolvent. In the former process, the precipitated particles are filtered,washed and dried. In the latter process, the reaction solution is addedto water and mixed in a blender or homogenizer to precipitate the resinproduct and create particles of the desired size.

The acetalization is catalyzed by the use of an organic or inorganicacid in an amount that will effectively allow protonation to occur, butwill not significantly alter the final product by causing unwantedhydrolysis of the acetal groups.

Examples of suitable aldehydes useful in preparing the first cyclicacetal group of the binary acetal polymers described herein include:

formaldehyde

acetaldehyde

propionaldehyde

n-butyraldehyde

isobutyraldehyde

4-hydroxybutyraldehyde

n-valeraldehyde

5-hydroxyvaleraldehyde

n-caproaldehyde

n-heptaldehyde

and the like.

Examples of suitable aldehydes useful in preparing the second cyclicacetal group of the binary acetal polymers described herein include:

2-phenyl propionaldehyde

3-phenyl butyraldehyde

benzaldehyde

2-hydroxy benzaldehyde

4-hydroxy benzaldehyde

2,4-dihydroxy benzaldehyde

cinnamaldehyde

hydrocinnamaldehyde

biphenyl carboxaldehyde

indole carboxaldehyde

salicylaldehyde

piperonal

furfural

and the like.

An especially preferred binary acetal polymer for use in this inventioncomprises about 7 mole % of vinyl alcohol moieties, about 12 mole % ofvinyl acetate moieties, about 27 mole % of cyclic acetal moietiesderived by reaction with propionaldehyde, and about 54 mole % of cyclicacetal moieties derived by reaction with 3-phenyl butyraldehyde.

Another especially preferred binary acetal polymer for use in thisinvention comprises about 7 mole % of vinyl alcohol moieties, about 12mole % of vinyl acetate moieties, about 27 mole % of cyclic acetalmoieties derived by reaction with n-butylraldehyde, and about 54 mole %of cyclic acetal moieties derived by reaction with benzaldehyde.

Polyvinyl alcohols suitable for use as starting materials in thisinvention are well known commerically available materials. Theypreferably have an average molecular weight in the range of from about3,000 to about 120,000. Examples of suitable polyvinyl alcohols includethose available in a range of molecular weights from AIR PRODUCTSCORPORATION under the trademarks AIRVOL 203, AIRVOL 205, AIRVOL 523 andAIRVOL 540. Other suitable polyvinyl alcohols include those availablefrom HOECHST-CELANESE under the trademarks MOWIOL 4-88, MOWIOL 5-88,MOWIOL 18-88, MOWIOL 26-88, and MOWIOL 40-88.

The novel binary acetal polymers described herein can be employed withany of the diazo resins known to be useful in lithographic printingplates. These include, for example, the condensation product of p-diazodiphenyl amine and paraformaldehyde, the condensation product of3-methoxy-4-diazo diphenylamine and paraformaldehyde, and the diazoresins of U.S. Pat. Nos. 2,063,631, 2,667,415, 2,667,498, 2,922,715,2,946,683, 3,050,502, 3,163,633, 3,227,074, 3,311,605, 3,406,159,3,679,419, 3,849,392 and 3,867,147.

The diazo resin is typically employed in an amount of about 20 to about60 percent by weight of the photosensitive layer, more preferably in anamount of from about 25 to about 50 percent by weight, and mostpreferably in an amount of about 30 to about 40 percent by weight. Thebinary acetal polymer is typically employed in an amount of about 30 toabout 80 percent by weight of the photosensitive layer, more preferablyin an amount of about 40 to about 70 percent by weight, and mostpreferably in an amount of about 50 to about 60 percent by weight.

In addition to a diazo resin and the binary acetal polymer, the imaginglayer of the lithographic printing plate can optionally contain avariety of other ingredients such as colorants, stabilizers, exposureindicators and surfactants. Particularly useful colorants are pigments,including phthalocyanine, anthraquinone and quinacridone pigments. Thepigment selected should be one which contains a minimal amount of heavymetal and which forms a stable dispersion with the binary acetal binderresin. Useful amounts of pigment are from about 1 to about 20 percent byweight of the photosensitive layer, more preferably from about 2 toabout 12 percent by weight, and most preferably from about 4 to about 8percent by weight. Effective stabilizers include both organic andinorganic acids, preferably citric, phosphoric, ascorbic or tartaricacids. Useful amounts of acid are from about 2 to about 6 percent byweight of the photosensitive layer, more preferably from about 2.5 toabout 5 percent by weight, and most preferably from about 3 to about 4percent by weight. Useful exposure indicators are dyes which are pHsensitive and which do not couple with diazonium compounds. Examples ofsuch dyes include eosin, azobenzene, Victoria Blue, 4-phenylazodiphenylamine, methyl violet and phenolphthalein. Useful amounts of thedye are from about 0.01 to about 3 percent by weight of thephotosensitive layer, more preferably from about 0.05 to about 2 percentby weight, and most preferably from about 0.1 to about 1 percent byweight. Useful surfactants include fluorocarbon surfactants, such asFC-430 surfactant from 3M Corporation or Zonyl NS surfactant fromDuPont, and silicone surfactants such as Silwet L-7606 surfactant fromUnion Carbide Corporation. The surfactant is used in an amount of fromabout 0.1 to about 4 percent by weight of the photosensitive layer, morepreferably from about 0.5 to about 2.5 percent by weight, and mostpreferably from about 1 to about 2 percent by weight.

In forming the photosensitive layer, the diazo resin, the binary acetalpolymer and the optional ingredients are dispersed in a suitable solventor mixture of solvents. Particularly useful solvents include2-methoxyethanol and the acetate thereof, 1-methoxy-2-propanol and theacetate thereof, 2-ethyoxyethanol and the acetate thereof,butyrolactone, methyl pyrrolidone, methyl lactate, ethyl acetate,dimethyl formamide, tetrahydrofuran, methylethyl ketone and butylacetate.

The support for the lithographic printing plate is typically formed ofaluminum which has been grained, for example by electrochemicalgraining, and then anodized, for example, by means of anodizingtechniques employing sulfuric acid and/or phosphoric acid. Methods ofboth graining and anodizing are very well known in the art and need notbe further described herein.

As previously indicated hereinabove, the novel binary acetal polymersdescribed herein can be employed in dual layer lithographic printingplates in which a radiation-sensitive layer comprising aphotocrosslinkable polymer is coated over a radiation-sensitive layercontaining a diazo resin. Photocrosslinkable polymers which areparticularly useful for this purpose are those containing thephotosensitive group --CH═CH--CO-- as an integral part of the polymerbackbone, especially the p-phenylene diacrylate polyesters. Thesepolymers are described, for example, in U.S. Pat. Nos. 3,030,208,3,622,320, 3,702,765 and 3,929,489. A typical example of such aphotocrosslinkable polymer is the polyester prepared from diethylp-phenylenediacrylate and 1,4-bis(β-hydroxyethoxy)cyclohexane, which iscomprised of recurring units of the formula: ##STR6##

Other particularly useful polymers of this type are those whichincorporate ionic moieties derived from monomers such asdimethyl-3,3'-[sodioimino)disulfonyl]dibenzoate anddimethyl-5-sodiosulfoisophthalate. Examples of such polymers includepoly[1,4-cyclohexylene-bis(oxyethylene)-p-phenylenediacrylate]-co-3,3'-[sodioimino)disulfonyl]dibenzoateandpoly[1,4-cyclohexylene-bis(oxyethylene)-p-phenylenediacrylate]-co-3,3'-[sodioimino)disulfonyl]dibenzoate-co-3-hydroxyisophthalate.

The novel binary acetal polymers described herein are especially usefulas binder polymers that are employed in combination with diazo resins inlithographic printing plates. However, they are also useful in otherapplications such as solvent thickeners, films with high tensile andshear strength and films which have a low dielectric constant. They canalso be used as a binder for matrices other than coatings.

The invention is further illustrated by the following examples of itspractice.

EXAMPLE 1

75.0 grams of AIRVOL 523 polyvinyl alcohol were added to a closedreaction vessel fitted with a water-cooled condensing column, followedby the addition of 225 grams of demineralized water and 450 grams ofn-propanol. With continual stirring, the mixture was cooked at 70° C.for 20 hours. After this time, the temperature was adjusted to 60° C.and 6.0 grams of concentrated hydrochloric acid was added. Over a 2 hourperiod, an admixture consisting of 10.91 grams of n-butyraldehyde and62.59 grams of benzaldehyde was slowly and uniformly added in a dropwisemanner. Upon complete addition of the mixture of aldehydes, the reactionwas continued at 60° C. for an additional 3 hours. At this point,potassium carbonate was added until a pH of 7.0±0.5 was obtained. Theneutralized reaction mixture was then added to 4.0 liters ofdemineralized water to precipitate the polymer product. Vigorous shearmixing was provided to form small particles as well as to remove then-propanol and neutralization by-products. The polymer was then vacuumfiltered and similarly washed two more times. After the third wash, theproduct was filtered and dried at 40° C. for 24 hours. 141.1 grams ofpolymer was obtained for a 95% yield. The structure of the polymer wasin accordance with the structural formula provided hereinabove in whichthe R₁ group is derived from n-butyraldehyde and has the formula --CH₂CH₂ --CH₃, the R₂ group is derived from benzaldehyde and has the formula##STR7## the value of n₁ is 7 mole %, the value of n₂ is 12 mole %, thevalue of n₃ is 27 mole % and the value of n₄ is 54 mole %.

The binary acetal polymer prepared as described above was utilized inpreparing a radiation-sensitive coating composition of the followingformulation:

    ______________________________________                                        Component           Weight %                                                  ______________________________________                                        Binary acetal polymer                                                                             1.50                                                      Diazo resin*        1.40                                                      Pigment (Toyo Lional Blue)                                                                        0.15                                                      Citric acid         0.20                                                      2-Methoxyethanol    76.70                                                     Demineralized water 20.00                                                     Surfactant (ZONYL FNS)                                                                            0.05                                                                          100.00                                                    ______________________________________                                         *Condensation product of 3methoxy-4-diazo diphenyl amine sulfate and an       isomeric mixture of methoxymethyl substituted diphenyl ethers isolated as     the diisopropylnaphthalene sulfonate salt.                               

The radiation-sensitive coating composition was filtered and coated onthe surface of an aluminum support which had been electrochemicallygrained, anodized and conditioned with a silicate barrier layer. Afterdrying of the radiation-sensitive layer was completed, a portion of theprinting plate was overlaid with a negative test target, exposed,developed and finished in accordance with conventional practice. Using asheet-fed press equipped with a conventional dampening system and acommercially available process black ink, the printing plate was rununtil image wear was observed. Solid areas became worn first, and wereconsidered unacceptable at 320,000 impressions. The highlight dots (0,5,1 and 2% at 150 lines/inch screen) were acceptable up to 470,000impressions.

To further assess the durability of the printing plate, it was floodexposed and then subjected to various solvents in order to quantifychemical resistance. A rating scale of one to five was used, where oneequates to essentially total removal of the coating and five equates tono coating removal and/or no coating attack.

Each of the following solvents was rubbed twenty times over a section ofthe plate. The plate was then rated for image attack.

methylene chloride (MCL)

methyl Cellosolve (MC)

methyl ethyl ketone (MEK)

butyrolactone (BLO)

isopropanol (IPA)

tetrahydrofuran (THF)

dimethylformamide (DMF)

toluene (T)

ethyl acetate (EA)

benzyl alcohol (BA)

The ratings for the plate described above were as follows:

    ______________________________________                                        MCL - 4    MC - 4      MEK - 4    BLO - 4                                     IPA - 4    THF - 4     DMF - 4    T - 4                                       EA - 3     BA - 3                                                             ______________________________________                                    

The results reported above indicate that the plate performed very wellfor both solvent resistance and press wear. Print quality and resolutionwere also very good.

EXAMPLES 2-10

The procedure reported in Example 1 was repeated in each of examples 2to 10 using the particular polyvinyl alcohols and aldehydes as indicatedin Table I. (PVOH represents polyvinyl alcohol). Printing plates wereprepared and evaluated in the same manner as described in Example 1, andthe results obtained are reported in Table II.

In each of examples 2 to 10, the composition of the binary acetalpolymer is described with reference to the mole percent hydroxylcontent, i.e., the mole percent of vinyl alcohol moieties, and the molepercent of moieties derived from the first and second aldehydes,respectively. The remainder to total 100 mole percent represents thevinyl acetate moieties.

                                      TABLE I                                     __________________________________________________________________________    Ex.                                                                              Starting Amount                                                                             First   Amount                                                                             Mole                                                                             Second  Amount                                                                             Mole                                                                             Mole %                       No.                                                                              PVOH     (grms)                                                                             Aldehye (grms)                                                                             %  Aldehyde                                                                              (grms)                                                                             %  Hydroxyl                     __________________________________________________________________________    2  AIRVOL 523                                                                             75.0 formaldehyde                                                                           9.78                                                                              43 benzaldehyde                                                                          34.56                                                                              43  3                           3  AIRVOL 205                                                                             75.0 acetaldehyde                                                                          11.00                                                                              32 4-hydroxy                                                                             45.75                                                                              49  7                                                            benzaldehyde                                 4  AIRVOL 523                                                                             50.0 n-heptaldehyde                                                                         8.70                                                                              15 2-phenylpro-                                                                          40.93                                                                              58 15                                                            pionaldehyde                                 5  MOWIOL 18-88                                                                           75.0 isobutyral-                                                                           12.92                                                                              23 salicylalde-                                                                          43.80                                                                              45 20                                            dehyde          hyde                                         6  AIRVOL 523                                                                             50.0 propionalde-                                                                           4.68                                                                              16 3-phenyl                                                                              47.66                                                                              62 10                                            hyde            butyraldehyde                                7  MOWIOL 5-88                                                                            75.0 n-valeralde-                                                                          13.76                                                                              17 2,4-dihydroxy-                                                                        66.24                                                                              66  5                                            hyde            benzaldehyde                                 8  AIRVOL 205                                                                             75.0 propionalde-                                                                          12.09                                                                              25 3-phenyl buty-                                                                        62.01                                                                              56  7                                            hyde            raldehyde                                    9  AIRVOL 540                                                                             50.0 n-butyralde-                                                                          12.42                                                                              38 hydrocinnamal-                                                                        23.12                                                                              38 12                                            hyde            dehyde                                       10 AIRVOL 523                                                                             50.0 formaldehyde                                                                           4.58                                                                              29 indole car-                                                                           33.17                                                                              44 15                                                            boxaldehyde                                  __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________    Example                                                                            Number of                                                                           Dots Held                                                                           Solvent Resistance                                           No.  Impressions                                                                         (percent)                                                                           MCL MC MEK BLO                                                                              IPA                                                                              THF                                                                              DMF T EA BA                              __________________________________________________________________________    2    455,000                                                                             0.5, 1, 2                                                                           4   3  4   5  4  5  4   4 4  4                               3    395,000                                                                             0.5, 1, 2                                                                           4   3  4   4  4  4  3   4 3  3                               4    460,000                                                                             0.5, 1, 2                                                                           4   3  4   4  4  4  3   4 3  3                               5    380,000                                                                             0.5, 1, 2                                                                           4   3  4   3  3  4  3   3 3  3                               6    485,000                                                                             0.5, 1, 2                                                                           4   3  3   4  3  4  3   3 3  3                               7    325,000                                                                             0.5, 1, 2                                                                           4   3  4   4  3  3  3   3 3  4                               8    380,000                                                                             0.5, 1, 2                                                                           4   3  4   5  4  5  4   4 4  4                               9    490,000                                                                             0.5, 1, 2                                                                           4   4  4   5  5  5  4   4 4  3                               10   470,000                                                                             0.5, 1, 2                                                                           4   4  4   4  4  3  4   4 3  3                               __________________________________________________________________________

As shown by the data in Table II, in each of Examples 2 to 10 thehighlight resolution was maintained throughout the run. The run lengthvaried, but was consistently above 300,000 impressions. Differences inrun length are, at least in part, attributable to variations inmolecular weight. Solvent resistance was good in all cases, and theplate performed in an acceptable manner.

COMPARATIVE EXAMPLES A TO F

Acetal polymers were prepared in a similar manner to that described inExample 1, but the aldehydes selected were such that the resultingpolymer was outside the scope of those defined by the structural formulapresented hereinabove. The acetal polymers utilized in this inventionare binary acetals, and one of the acetal groups is unsubstituted orsubstituted with an alkyl or hydroxyalkyl group while the other issubstituted with an aromatic or heterocyclic moiety. In comparativeExample A, the acetal polymer is a mono-acetal resulting from use offormaldehyde as the only aldehyde reactant. In comparative Examples B, Cand D, the acetal polymers are mono-acetals resulting from use ofn-butyraldehyde, benzaldehyde and 2-phenyl propionaldehyde,respectively, as the only aldehyde reactant. In comparative Example E,the acetal polymer is a binary acetal, but both aldehydes employed arealkyl aldehydes so the resulting polymer lacks the R₂ radical defined inthe aforesaid structural formula. In comparative Example F, the acetalpolymer is a binary acetal, but both aldehydes employed are arylaldehydes, so the resulting polymer lacks the R₁ radical defined in theaforesaid structural formula.

The aldehydes employed in comparative examples A to F are described inTable III and the results obtained are described in Table IV.

                                      TABLE III                                   __________________________________________________________________________    Ex.                                                                              Starting Amount                                                                             First  Amount                                                                             Mole                                                                             Second                                                                              Amount                                                                             Mole                                                                             Mole %                          No.                                                                              PVOH     (grms)                                                                             Aldehye                                                                              (grms)                                                                             %  Aldehyde                                                                            (grms)                                                                             %  Hydroxyl                        __________________________________________________________________________    A  AIRVOL 205                                                                             75.0 formaldehyde                                                                         18.78                                                                              81  --   --   --  7                              B  AIRVOL 523                                                                             75.0 n-butyralde-                                                                         38.72                                                                              68  --   --   -- 20                                               hyde                                                         C  AIRVOL 205                                                                             75.0 benzaldehyde                                                                         64.20                                                                              78  --   --   -- 10                              D  MOWIOL 5-88                                                                            75.0 2-phenylpro-                                                                         72.15                                                                              68  --   --   -- 20                                               pionaldehyde                                                 E  AIRVOL 205                                                                             75.0 acetaldehyde                                                                          8.89                                                                              26 n-butyral-                                                                          29.07                                                                              52 10                                                              dehyde                                        F  MOWIOL 40-88                                                                           75.0 benzaldehyde                                                                         32.10                                                                              39 hydrocinna-                                                                         40.60                                                                              39 10                                                              maldehyde                                     __________________________________________________________________________

                                      TABLE IV                                    __________________________________________________________________________    Example                                                                            Number of                                                                           Dots Held                                                                           Solvent Resistance                                           No.  Impressions                                                                         (percent)                                                                           MCL MC MEK BLO                                                                              IPA                                                                              THF                                                                              DMF T EA BA                              __________________________________________________________________________    A    210,000                                                                             2% only                                                                             3   2  3   3  2  3  2   2 1  1                               B    185,000                                                                             2% only                                                                             3   1  3   3  3  2  2   3 2  2                               C    180,000                                                                             2% only                                                                             3   2  3   2  3  3  3   3 2  1                               D    170,000                                                                             2% only                                                                             2   1  2   3  3  2  2   2 1  1                               E    175,000                                                                             2% only                                                                             1   1  2   2  2  2  1   2 1  1                               F    205,000                                                                             2% only                                                                             3   2  3   2  2  3  2   2 2  1                               __________________________________________________________________________

As shown by the data in Table IV, the results obtained in comparativeexamples A to F were greatly inferior to those obtained in the examplesof the invention, both in regard to run length and solvent resistance.

COMPARATIVE EXAMPLES G TO L

Commercially available lithographic printing plates were evaluated inthe same manner as described above in order to compare their performancewith that of lithographic printing plates utilizing the novel binaryacetal resins described herein.

The printing plates evaluated were as follows:

Comparative Example G--KODAK KNA3 printing plate

Comparative Example H--POLYCHROME VISTAR M printing plate

Comparative Example I--FUJI FND printing plate

Comparative Example J--3M VIKING GM printing plate

Comparative Example K--DUPONT HOWSON AQ III printing plate

Comparative Example L--ENCO AN-61 printing plate.

The results obtained are reported in Table V below.

                                      TABLE V                                     __________________________________________________________________________    Example                                                                            Number of                                                                           Dots Held                                                                           Solvent Resistance                                           No.  Impressions                                                                         (percent)                                                                           MCL MC MEK BLO                                                                              IPA                                                                              THF                                                                              DMF T EA BA                              __________________________________________________________________________    G    260,000                                                                             1 & 2%                                                                              2   3  3   3  3  3  3   2 3  3                               H    155,000                                                                             2% only                                                                             1   1  2   3  3  3  2   2 2  2                               I    210,000                                                                             1 & 2%                                                                              1   1  2   2  2  2  1   2 1  1                               J    140,000                                                                             2% only                                                                             2   1  3   3  3  3  2   2 1  1                               K    145,000                                                                             >5%   1   1  1   2  3  2  1   2 1  1                               L    225,000                                                                             1 & 2%                                                                              2   2  3   3  3  3  2   3 2  2                               __________________________________________________________________________

As shown by the data in Table V, the results obtained in comparativeexamples G to L were greatly inferior to those obtained in the examplesof the invention both in regard to run length and solvent resistance. Incomparison to printing plates prepared from the novel binary acetalpolymers described herein, the commercially available printing plates donot run as long nor do they have equal ability to hold the highlightdots.

The invention has been described in detail, with particular reference tocertain preferred embodiments thereof, but it should be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

I claim:
 1. A photosensitive composition comprising a mixture of (1) adiazo resin and (2) a binary acetal polymer; said binary acetal polymerhaving recurring units represented by the formula: ##STR8## wherein R₁is --H or --C_(n) H_(2n+1) or --C_(n) H_(2n) --OH where n=1-12R₂ is##STR9## where R₃ is ##STR10## and x=0-8 m=0-8 y=0-8 p=0-8 R₄ =--H,--R₅, ##STR11## in which Y=--O--, --S--, ##STR12## --CH₂ --, --NH-- or##STR13## R₅ =--OH, --CH₂ OH, --OCH₃, --COOH or --SO₃ H z=1 to 3 and n₁=0-25 mole % n₂ =2-25 mole % n₃ =10-60 mole % n₄ =35-80 mole %
 2. Aphotosensitive composition as claimed in claim 1 wherein n₁ is equal to5 to 15 mole %, n₂ is equal to 5 to 15 mole %, n₃ is equal to 15 to 35mole % and n₄ is equal to 45 to 70 mole %.
 3. A photosensitivecomposition as claimed in claim 1 wherein R₁ is --H, --CH₂ CH₃, --CH₂CH₂ CH₃, --(CH₂)₃ CH₃, ##STR14## --(CH₂)₄ CH₃ or --(CH₂)₆ CH₃
 4. Aphotosensitive composition as claimed in claim 1 wherein R₂ is ##STR15##5. A photosensitive composition as claimed in claim 1 wherein R₂ is##STR16##
 6. A photosensitive composition as claimed in claim 1 whereinR₂ is ##STR17##
 7. A photosensitive composition as claimed in claim 1wherein R₁ is --CH₂ CH₃ and R₂ is ##STR18##
 8. A photosensitivecomposition as claimed in claim 1 wherein R₁ is --CH₂ CH₃ and R₂ is##STR19##
 9. A photosensitive composition as claimed in claim 1 whereinsaid diazo resin is a condensation product of 3-methoxy-4-diazo diphenylamine sulfate and an isomeric mixture of methoxymethyl substituteddiphenyl ethers.
 10. A photosensitive composition comprising a mixtureof (1) a diazo resin and (2) a binary acetal polymer; said binary acetalpolymer having recurring units represented by the formula: ##STR20##wherein n₁ is about 7 mole %, n₂ is about 12 mole %, n₃ is about 27 mole%, and n₄ is about 54 mole %.
 11. A photosensitive compositioncomprising a mixture of (1) a diazo resin and (2) a binary acetalpolymer; said binary acetal polymer having recurring units representedby the formula: ##STR21## wherein n₁ is about 7 mole %, n₂ is about 12mole %, n₃ is about 27 mole % and n₄ is about 54 mole %.
 12. Alithographic printing plate comprising a support having thereon aradiation-sensitive layer comprising a diazo resin and a polymericbinder; said polymeric binder being a binary acetal polymer havingrecurring units represented by the formula: ##STR22## wherein R₁ is --Hor --C_(n) H_(2n+1) or --C_(n) H_(2n) --OH where n=1-12R₂ is ##STR23##where R₃ is --(--CH₂ --)_(x) -- or ##STR24## and x=0-8 m=0-8 y=0-8 p=0-8R₄ =--H, --R₅, ##STR25## in which Y=--O--, --S--, ##STR26## --CH₂ --,--NH-- or ##STR27## R₅ =--OH, --CH₂ OH, --OCH₃, --COOH or --SO₃ H z=1 to3 and n₁ =0-25 mole % n₂ =2-25 mole % n₃ =10-60 mole % n₄ -35-80 mole %13. A lithographic printing plate as claimed in claim 12 wherein n₁ isequal to 5 to 15 mole %, n₂ is equal to 5 to 15 mole %, n₃ is equal to15 to 35 mole % and n₄ is equal to 45 to 70 mole %.
 14. A lithographicprinting plate as claimed in claim 12 wherein R₁ is --H, --CH₂ CH₃,--CH₂ CH₂ CH₃, --(CH₂)₃ CH₃, ##STR28## --(CH₂)₄ CH₃ or --(CH₂)₆ CH₃ 15.A lithographic printing plate as claimed in claim 12 wherein R₂ is##STR29##
 16. A lithographic printing plate as claimed in claim 12wherein R₂ is ##STR30##
 17. A lithographic printing plate as claimed inclaim 12 wherein R₂ is ##STR31##
 18. A lithographic printing plate asclaimed in claim 12 wherein R₁ is --CH₂ CH₃ and R₂ is ##STR32##
 19. Alithographic printing plate as claimed in claim 12 wherein R₁ is --CH₂CH₃ and R₂ is ##STR33##
 20. A lithographic printing plate as claimed inclaim 12 wherein said diazo resin is a condensation product of3-methoxy-4-diazo diphenyl amine sulfate and an isomeric mixture ofmethoxymethyl substituted diphenyl ethers.
 21. A lithographic printingplate as claimed in claim 12 wherein said support is comprised ofgrained and anodized aluminum.
 22. A lithographic printing plate asclaimed in claim 12 wherein said radiation-sensitive layer is comprisedof about 25 to about 50 percent by weight of said diazo resin and about40 to about 70 percent by weight of said binary acetal polymer.
 23. Alithographic printing plate as claimed in claim 12 wherein saidradiation-sensitive layer additionally comprises about 2 to about 12percent by weight of pigment, about 2.5 to about 5 percent by weight ofan acid which functions as a stabilizer, about 0.05 to about 2 percentby weight of a dye which functions as an exposure indicator, and about0.5 to about 2.5 percent by weight of a surfactant.
 24. A lithographicprinting plate comprising a support having thereon a radiation-sensitivelayer comprising a diazo resin and a polymeric binder; said polymericbinder being a binary acetal polymer having recurring units representedby the formula: ##STR34## wherein n₁ is about 7 mole %, n₂ is about 12mole %, n₃ is about 27 mole %, and n₄ is about 54 mole %.
 25. Alithographic printing plate comprising a support having thereon aradiation-sensitive layer comprising a diazo resin and a polymericbinder; said polymeric binder being a binary acetal polymer havingrecurring units represented by the formula: ##STR35## wherein n₁ isabout 7 mole %, n₂ is about 12 mole %, n₃ is about 27 mole %, and n₄ isabout 54 mole %.
 26. A lithographic printing plate comprising a grainedand anodized aluminum support having thereon a first radiation-sensitivelayer comprising a diazo resin and a polymeric binder and a secondradiation-sensitive layer comprising a photocrosslinkable polymer; saidbinder being a binary acetal polymer having recurring units representedby the formula: ##STR36## wherein R₁ is --H or --C_(n) H_(2n+1) or--C_(n) H_(2n) --OH where n=1-12R₂ is ##STR37## where R₃ is --(--CH₂--)_(x) -- or ##STR38## and x=0-8 m=0-8 y=0-8 p=0-8 R₄ =--H, --R₅,##STR39## in which Y=--O--, --S--, ##STR40## --CH₂ --, --NH-- or##STR41## R₅ =--OH, --CH₂ OH, --OCH₃, --COOH or --SO₃ H z=1 to 3 and n₁=0-25 mole % n₂ =2-25 mole % n₃ =10-60 mole % n₄ =35-80 mole %.